1. Field of the Invention
The present invention relates to a splashing oil lubrication type internal combustion engine and more particularly to a splashing oil lubrication type internal combustion engine capable of reducing temperature of engine oil by raising a cooling efficiency of a crankcase.
2. Background Art
An example of the splashing oil lubrication type internal combustion engine disclosed in Japanese Patent Application Laid-open No. Toku-Kai-Hei 10-280932 has a method of splashing oil stored below in a crankcase by an oil dipper equipped with a connecting rod and another example of the engine disclosed in Japanese Patent Application Laid-open No. Toku-Kai-Hei 8-177441 has a method of splashing oil by an oil dipper rotating in an interlocking relationship with a crankshaft.
FIG. 4 is a front sectional view of a splashing oil lubrication type engine according to the prior art. An engine 1 has a cylinder block 2 integrally formed with a crankcase 4 and including a cylinder 3. The crank case 4 comprises a bottom section 11, a rear wall section 12 extending upwardly from the rear (back side of the drawing) end of the bottom section 11, side wall sections 13, 14 extending upwardly from the left and right end of the bottom section 11 respectively and connecting with the left and right ends of the rear wall section 12 respectively, a ceiling section 15 closing upper ends of the rear wall section 12, the side wall sections 13, 14, and a crank chamber 16 enclosed by these bottom section 11, side wall sections 13, 14, ceiling section 15 and a crank case cover (not shown) formed on the front side of the crank case 4.
A crank shaft 18 extending in an orthogonal direction with respect to the drawing is rotatably supported at the rear end thereof by a bearing 18 formed at a specified vertical position of the rear wall section 12 and supported at the front end thereof by a bearing (not shown) provided at the same vertical position of the crank case cover. A crank pulley 19 is coaxially secured to the front end of the crankshaft 18. The crank pulley 19 has teeth on the periphery surface thereof to mesh with teeth of a timing belt 26 wound around the crank pulley 19 and a camshaft pulley 25 which will be described hereinafter.
The cylinder 3 of the cylinder block 2 has a cylinder axis 5 slanted with respect to the vertical direction of the engine 1 so that the axis 5 extends above diagonally from the upper portion of the right wall section 14 of the crankcase 4. The cylinder 3 is connected at the upper end thereof with a cylinder head 21 having a valve train mechanism 22. Further, at the front of the cylinder 3, there is provided a belt chamber 23 communicating between the crank chamber 16 and a valve train chamber of the cylinder head 21. The valve train mechanism 22 has a camshaft 24 extending in the same direction as the crankshaft 18. The camshaft pulley 25 is coaxially secured to the front end of the camshaft 24 and has teeth meshing with the teeth of the timing belt 26.
The timing belt 26 is constituted by fabric core material such as carcass, lubber and synthetic resin and has equally spaced step-like teeth formed on the inner periphery surface of the belt. Further, the timing belt 26 is housed in the belt chamber 23 and wound around the crank pulley 19 and the cam pulley 25 so as to rotate the cam shaft 24 in an interlocking relationship with the rotation of the crankshaft 18.
However, the engine according to the prior art as described above is not designed so as to reduce temperature inside of the crank chamber 16 or to reduce temperature of engine oil splashed in the crank chamber 16 or engine oil stored in the lower part of the crank chamber 16. Accordingly, in case where temperature of the crank chamber 16 becomes high, temperature of engine oil is also increased and as a result its lubrication characteristic goes down.
Further, there is a fear that splashed engine oil in high temperature sticks to the timing belt 26 and as a result heat deteriorates the timing belt 26.
It is an object of the present invention to provide a splashing oil lubrication type internal combustion engine capable of reducing temperature of the crank chamber 16 and lowering the temperature of engine oil. Particularly, as well known, the lowering of engine oil is very important for maintain the lubrication characteristic of engine oil in good condition, that is, for preventing the lubrication performance for lubricating miscellaneous components, such as a crankshaft, a connecting rod, intake and exhaust valves and a valve driving mechanism, from being degraded. It is another object of the present invention to provide a splashing oil lubrication type internal combustion engine in which a timing belt of the engine can be protected from deterioration due to heat received from engine oil.
In accordance with a first aspect of the invention, the object is achieved by absorbing heat in a crank chamber as much as possible. For that purpose, the engine comprises an oil splashing means for splashing engine oil in the crank chamber in a radial direction of a crankshaft and for forming a flow of splashing oil around the crankshaft and a plurality of heat receiving ribs projected inwardly from the inner wall surface of the crankcase so as to absorb heat in the crank chamber.
A second aspect of the present invention is to provide an engine capable of discharging heat the crankcase as much as possible. For that purpose, the engine includes a plurality of heat radiating ribs projected outwardly from the outer wall surface of the crankcase so as to discharge heat in the crank chamber out of the engine.
Further, a third aspect of the present invention is to provide heat receiving ribs on the inner wall surface of the crankcase and at the same time to provide heat radiating ribs on the outer wall surface of the crankcase so as to further enhance the heat discharge from the crankcase.